Striking mechanisms are amongst the most prized complications in fine horology. Integrating such mechanisms in a watch is always complex.
Generally, conventional grande sonnerie mechanisms have two gongs, a lower pitched “dong” used for striking the hours, and combined with a higher pitched “ding” for striking each quarter “ding-dong”, this higher pitched gong can also be used for striking the minutes if the watch is equipped to do so.
A grande sonnerie mechanism with a carillon or chimes is designed to play a short melody at every quarter-hour, and on the full hour. In the most elaborate carillons, a different melody is played for each quarter-hour. And the melody played on the hour is the sequence resulting from the individual quarter-hour melodies.
It is difficult to play a melody at a precise time. The surprise-piece provides better precision as regards the instant at which the strike function starts. In order to avoid any error during striking an extremely precise adjustment must be made of the components, for example to make a stylus cooperate with a notch: such a mechanism is very difficult to adjust, and any shock may impair this adjustment.
One alternative could consist in making the snails larger, with a modification of their time period. However, the space available, which depends on the other complications, does not always permit such an arrangement.
EP Patent Application No 1416342A1 in the name of NOUVELLE LEMANIA SA discloses a striking timepiece comprising a centre wheel set that makes one revolution per hour and is provided with a first snail and a surprise-piece associated with the latter, a second snail, a pivoting rack connected to a striking work control member and provided with a feeler arranged to abut against the second snail when the striking work control member is actuated, a surprise-piece jumper for pivoting the surprise-piece onto the first snail, and a surprise-piece isolator device that keeps the surprise-piece jumper away from the surprise-piece when the rack is in the rest position. This surprise-piece isolator device includes a projecting element fixed to the rack, and arranged to cooperate with the surprise-piece jumper to move the latter away from the surprise-piece.
CH Patent Application No 704590A2 in the name of MONTRES BREGUET SA discloses an isolating mechanism for a timepiece, including, on the one hand, a timepiece movement and, on the other hand, at least one striking mechanism including feeler arms for reading time information, on time references driven by said timepiece movement. This isolating mechanism includes at least a first isolator, arranged to cooperate with a control mechanism of the timepiece, in order, in a first armed position, to adopt a stop position that prevents the time information feelers from searching for information on the time references, and, in a second unarmed position, to allow the passage of the feelers to come into contact with the time references.